Project Summary The proposed project addresses a critical gap in scientific knowledge concerning comorbidities between internalizing mental health and developmental disability symptoms in adolescence, focusing specifically on autism symptoms (e.g., sensory sensitivities, irritability, repetitive behaviors) and emotion regulation difficulties. This is an area of high importance for NIH due to its ability to inform translational public health research and improve care within these families. This project and training plan is innovative by targeting internalizing and autism symptoms in boys from a developmental perspective?examining puberty as a life stage during which many symptom types may become exacerbated by the biopsychosocial changes happening within the body and brain. The project considers sex as a biological variable by focusing on boys?for whom research on puberty and internalizing symptoms remain understudied and prevailing models of risk, developed for girls, may not be applicable. Aim 1 will investigate internalizing symptoms in boys during puberty, particularly early stages of puberty. Utilizing data from the Wisconsin Twin Project (WTP; age 7, N=1,613; 14, N=859; 16 years old, N=207), longitudinal multi-level models will examine the association between pubertal maturation, including sex hormones, and internalizing symptoms over time in boys. Using the National Database for Autism Research (NDAR), Aim 2 will investigate the association between internalizing and autism symptoms during puberty in autistic boys (ages 8-18 years; N=346) using cross-sectional regression models. Aim 3 explores secondary regression analysis of puberty with autism and internalizing symptoms in 25 neurotypical and 25 autistic adolescent boys (ages 11-17 years) using the Social Conscious Emotions (SCE) study. The SCE dataset expands past NDAR by including a wide range of relevant measures including pubertal hormones, internalizing symptoms, and autism symptoms. To accomplish these aims, Dr. Elizabeth Shirtcliff will be the primary training mentor due to her extensive knowledge on pubertal maturation, psychophysiology, and psychopathology. Drs. Goldsmith (co-sponsor) and Mazefsky will provide expert mentorship and guidance on mental health issues and developmental disabilities, specifically autism. Mentorship from Drs. Jennifer Pfeifer, Carol Van Hulle, Mrs. Judith Ursitti, and targeted webinars and conferences (i.e., Autism Research Institute, Interagency Autism Coordinating Committee, Society of Research on Adolescence, Wisconsin Symposium on Emotion) will complete the experiential, didactic and mentored training needed to learn trajectories of early developmental processes to puberty, advanced longitudinal models and using large databases, and translation of research to public policies. This combination of experiential training and targeted support from my mentorship team will leave me poised to attain my long-term goal to be a developmental scientist with an expertise on adolescent health and developmental disabilities.